The present invention relates to a speaker edge at the circumferential edge of a cone body (also referred to as a xe2x80x9cspeaker diaphragm bodyxe2x80x9d).
In a speaker having a general configuration, as shown in FIG. 5, a cone body 50 composed of cone paper is retained on a frame F through a speaker edge 60 which is provided at the circumferential edge of the cone body, so that the cone body 50 is not prevented from vibrating. Incidentally, in order to not prevent the cone body 50 from vibrating, this speaker edge 60 is shaped so that a bent portion 65, bent upward or downward with a sectionally arc shape, is formed between an inner circumferential edge 61 and an outer circumferential edge 63.
In the background art, as such a speaker edge, there are: a speaker edge formed in such a manner that a foamed rubber composition is molded in a mold; a speaker edge formed in such a manner that molten resin of thermoplastic resin, for example, acrylic resin, polycarbonate resin, thermoplastic polyurethane resin, or the like, is injection-molded in a mold where a cone body is disposed; a speaker edge formed in such a manner that foamed polyurethane slavstock formed into a block by foam molding is cut out into a sheet with a predetermined thickness, and the foamed polyurethane sheet is shaped into the form of a speaker edge by heat compression with a press die; and so on.
However, the background-art speaker edges have problems as follows. First, in the speaker edge formed in such a manner that a foamed rubber composition is molded in a mold cavity, there is a problem that it is so heavy that the mass of a vibration system becomes heavy when the speaker edge is used in adhesion to a cone body. As a result, the sound pressure-frequency characteristic deteriorates. In addition, in the rubber speaker edge, there is another problem that high technology is required for bonding the speaker edge with a cone body.
In addition, in the speaker edge formed by injection molding out of molten thermoplastic resin, there is a problem that the temperature of the molten resin is about 200 to 300xc2x0 C. which is so high that a cone body is apt to be damaged by heat when the speaker edge is molded integrally with the cone body in a mold.
In addition, in the speaker edge formed in such a manner that a slab of foamed polyurethane is cut out into a sheet and the foamed polyurethane sheet is molded by heat compression (hereinafter abbreviated to xe2x80x9cslab cut-out heat compression moldingxe2x80x9d), the outer sides (convex sides) of bent base portions 66 and 67 shown in FIG. 5 are extended on a larger scale at the time of heat compression by press molding so as to be low in density, while the opposite inner sides (concave sides) are compressed so as to be high in density. The state of density of such an uneven surface results in deterioration of strength. Thus, the speaker edge is not preferable in view of durability or the like. Particularly, in the speaker edge, the inner circumferential side of the speaker edge 60 vibrates together with the circumferential edge of the cone body 50, while the outer circumferential side of the speaker edge 60 is bound on the frame F. As a result, fatigue is concentrated on the frame-side bent base portion 67. Thus, in the speaker edge formed by slab cut-out heat compression molding, the strength of the bent base portion is not sufficient.
In addition, the above-mentioned foamed urethane sheet is cut out of a slab so as to have an even thickness, and molded by heat compression. Accordingly, there is a problem that a required portion of the speaker edge cannot be made to have an optimum thickness, for example, the bent base portions 66 and 67 where the strength is lowered in the above-mentioned compression molding cannot be thickened to enhance the strength.
In addition, the above-mentioned foamed urethane slab cannot help the fact that the density differs from one portion to another when the slab is foamed and produced. Thus, the foamed polyurethane sheet cut out of the slab differs in density from one cut-out position thereof to another. As a result, there is a problem that the speaker edge formed out of the cut-out foamed polyurethane sheet by heat compression molding varies widely in the lowest resonance frequency f0 of the speaker so that the quality is hardly fixed. When the scattering of f0 was measured in practice, it was xc2x115 Hz at N=100.
Further, in a speaker, or the like, which is disposed in a door of a car, waterproofness is required of the speaker edge. However, since the above-mentioned foamed polyurethane slab has such a property that water penetrates from the surface, there is a problem that the speaker edge formed by slab cut-out heat compression molding is also inferior in waterproofness. In order to solve this problem of waterproofness, there has been also proposed a speaker edge coated with fluororesin. Also in this speaker edge coated with fluororesin, however, since the coating has an open-cell cellular structure, it is not practical to coat the speaker edge thick enough to close aperture portions. It is therefore impossible to say that the waterproofness is ensured sufficiently. In addition, there is a problem that the cost increases.
In addition, in the above-mentioned speaker edge formed by slab cut-out heat compression molding, as shown in the expanded schematic view of FIG. 6 which shows a section of an edge, the vicinity of a surface 65a is compressed at the time of heat compression molding, so that a hard and high-density skin layer 68 in which each cell H has been collapsed is formed through a clear boundary surface 68a between the skin layer 68 and a foamed layer 69 inside the skin layer 68. Thus, since the physical properties change clearly and suddenly, the amplitude in resonance increases so that an undesired phenomenon is produced.
Taking the foregoing problems into consideration, it is an object of the present invention to provide a speaker edge which is high in strength, less in scattering of f0, high in waterproofness, small in amplitude in resonance, easy to mold, reliable and easy to be integrated with a cone body.
According to the present invention, there is provided a speaker edge constituted by a molding which is molded in a manner so that a speaker edge raw material composition containing isocyanate and polyol is injected into a cavity of a mold by an agitating/mixing apparatus and subjected to reaction, foaming and curing the mold. The speaker edge raw material composition to be used for casting according to the present invention may be used in combination of ones suitably selected from formula systems applied for various purposes as polyurethane raw material compositions. So-called soft hot mold formula systems which are known, semi-rigid cold mold formula systems, or formula systems suitable for mechanical froth meatbod may be applied to molding.
(2) Further, the present invention is characterized in that the speaker edge raw material composition is injected into the molding cavity in which a cone body is disposed, and the speaker edge molded by reaction, foaming and curing of the raw material composition is bonded integrally with the cone body by chemical reaction at the time of the reaction, foaming and curing.
(3) Further, the present invention is characterized in that a composition having viscosity in a range of from 100 cps to 100,000 cps at room temperature immediately after mixing is used as the speaker edge raw material composition.
(4) Further, the present invention is characterized in that the polyol is composed of a mixture of polyether polyol and polypolyester polyol.
(5) Further, the present invention is characterized in that cell inside the speaker edge is composed of only closed cells or both closed and open cells.
(6) Further, the present invention is characterized in that a surface of the speaker edge is composed of a skin layer to which a mold surface of the mold is transferred.
(7) Further, the present invention is characterized in that the skin layer of the surface is formed integrally with an inside foamed layer without any clear boundary surface lying therebetween.
(8) Further, the present invention is characterized in that density in thin base portions of a bent portion is higher than that in other thick portions.
(9) Further, the present invention is characterized in that density of the speaker edge is in a range of from 0.15 g/cm3 to 0.9 g/cm3.